1. Field of the Invention
The present invention relates in general to Global Positioning System (GPS) receivers, and in particular to a method and apparatus for transmitting position data using control channels in wireless networks.
2. Description of the Related Art
Cellular telephony, including Personal Communication System (PCS) devices, has become commonplace. The use of such devices to provide voice, data, and other services, such as internet access, has provided many conveniences to cellular system users.
A current thrust in the cellular and PCS arena is the integration of Global Positioning System (GPS) technology into cellular telephone devices and other wireless transceivers. For example, U.S. Pat. No. 5,874,914, issued to Krasner, which is incorporated by reference herein, describes a method wherein the base station (also known as the Mobile Telephone Switching Office (MTSO)) transmits GPS satellite information, including Doppler information, to a remote unit using a cellular data link, and computing pseudoranges to the in-view satellites without receiving or using satellite ephemeris information.
This current interest in integrating GPS with cellular telephony stems from a new Federal Communications Commission (FCC) requirement that cellular telephones be locatable within 20 feet once an emergency call, such as a “911” call (also referred to as Enhanced 911 or “E911”) is placed by a given cellular telephone. Such position data assists police, paramedics, and other law enforcement and public service personnel, as well as other agencies that may need or have legal rights to determine the cellular telephone's position. Further, GPS data that is supplied by the MTSO in the Krasner system can be used by the cellular user for directions, location of other locations that the cellular user is trying to locate, determination of relative location of the cellular user to other landmarks, and directions for the cellular user via internet maps or other GPS mapping techniques, etc. Such data can be of use for other than E911 calls, and would be very useful for cellular and PCS subscribers.
The approach in Krasner, however, is limited by the number of data links that can be connected to a GPS-dedicated data supply warehouse. Such a server/GPS data supply location, whether at the MTSO or other locations in the cellular network, would require the cellular telephone to maintain two data links; one for voice and/or cellular subscriber data for use by the cellular subscriber to transmit and receive voice and/or data that the cellular subscriber is using, e.g., talking with another person, sending data across the cellular network, etc., and one for the GPS information that is being sent by the MTSO/cellular network server to the cellular subscriber. Cellular telephones are not currently capable of operating in such a manner, and, in essence, would be required to maintain two voice/data links simultaneously, and/or switch between two data links in time; one line for the cellular user to use to transmit their own voice and/or data, and one line for the GPS data link. This would result in higher charges for the cellular subscriber, as well as overloading the cellular system's available bandwidth. In essence, GPS-equipped telephones, once deployed in a cellular system described by Krasner, would require twice as much bandwidth as the present cellular system, where bandwidth is already overloaded. Alternatively, additional cells could be installed in a Krasner-based system, which would increase the capital outlay for the cellular telephone network.
Further, Krasner admits limitations on the location of the “base station” as being required to be within 150 kilometers of the cellular subscriber at the time the cellular subscriber is using the wireless handset. When a cellular subscriber is roaming outside of the home service area, or the MTSO is located at a centralized site for a large cellular network, such as with the two largest cellular networks currently in service in the United States, namely, AT&T and Verizon Wireless, the Krasner system would require additional MTSO sites throughout such networks, making the networks more costly and less efficient. As such, the FCC mandate for E911 calls would be difficult if not impossible to achieve using the Krasner system, or any other system currently proposed.
It can be seen, then, that there is a need in the art for delivering GPS data to cellular and PCS subscribers without using a cellular data (voice) link. It can also be seen that there is a need in the art for GPS-capable cellular and PCS telephones. It can also be seen that there is a need in the art for GPS-capable cellular and PCS telephones that can receive GPS satellite data for use by the cellular/PCS subscriber. It can also be seen that there is a need in the art for a large cellular system that can use and/or supply GPS information to cellular users without the requirement of geographically proximate base stations.